Abstract
During the operation of load cell, heat is generated by the strain gauge and the electronics on the PCB board, which leads to temperature gradients within the sensor itself. These temperature gradients are unstable at different ambient temperatures. Compensation inaccuracies can also occur when compensating for sensor measurements at different temperatures This paper proposes a method to change the position of temperature compensation resistors to address errors caused by the temperature field effect of the strain gauge sensor itself. Without affecting the sensor’s strain measurement, the correctness of the proposed method is demonstrated through steady-state thermal simulation results in ANSYS and experimental results, effectively addressing errors caused by unstable temperature gradients during the operation of strain gauge sensors.
Introduction
The load cell, also known as a force sensor, has the advantages such as high precision, high reliability, high sensitivity, high linearity, small size, and mature manufacturing technology, and is widely used in robotics, medicine, agronomy, vehicle science and other fields.
However, during the production and use of load cells, many performance compensations are required, including hysteresis compensation, creep compensation, zero compensation, and sensitivity improvement. When the external temperature changes, the thermal expansion and contraction effects and residual stress will affect the performance of the load cell. The performance of the load cell varies at different temperatures, which leads to the complexity of sensor compensation. According to OIML R60 regulations, as long as the performance compensation at -10℃, 20℃, and 40℃ is within the acceptable range, the performance compensation of the load cell is considered to be up to standard. Luo L et al. showed that within a certain temperature range, the output voltage, output linearity, and sensitivity of the load cell decrease with increasing temperature, and temperature compensation is performed on the sensor according to the principle of double Wheatstone bridge compensation. Dadasikandar K et al.studied the use of polysilicon as a piezoresistive material for measuring pressure in high-temperature environments, conducted relevant simulations from the perspective of materials, and improved the sensitivity and other performance of the sensor.
Yi J H studied the factors affecting the thermal effects of load cells, including different strain gauge resistances, unequal lengths of Wheatstone bridges, and different TCRs (Temperature Coefficient of Resistance) of thermal compensation resistor nickel sheets. The results showed that it is impractical to include TCR differences in compensation, and proposed inserting a thermistor into one of the four bridge arms to compensate for zero drift caused by temperature. Yi J H et al.also proposed connecting a thermistor in series with the bridge circuit to compensate for the zero point of the Wheatstone bridge. The results showed that as long as the TCR of the temperature compensation resistor is greater than the TCR of the zero balance resistor, the two temperature output ratio differences obtained by the iterative method converge to zero. Du D L et al. analyzed the nonlinear relationship between the thermal resistance changes of different materials and expansion mismatch, and experimentally verified that the temperature characteristic curve is also nonlinear. Hui Chao Shi et al. proposed a temperature compensation method based on artificial neural networks (ANN) to reduce the additional temperature drift of the resonant frequency caused by electrothermal excitation and environmental temperature changes.
Wang S et al. proposed a temperature compensation method based on backpropagation neural networks (BP-NN) and introduced genetic algorithms to improve BP neural networks, effectively improving temperature compensation. Based on the above literature, this paper studies the changes in the temperature gradient caused by the self-heating of the load cell, changes the position of the compensation resistor without affecting the strain of the elastomer, and provides a new idea for the temperature compensation of the load cell. Compared with the above compensation methods, this paper starts from the core of temperature compensation: the position of the compensation resistor, changes the position of the compensation resistor, and thus obtains more accurate compensation.
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